I have 4x4 Planes subidivided , i would like to sculpt them all at the same time so the remain connected at the edges
OK. Bringing the comments to an answer.

Create the plane, enter Edit Mode and subdivide it once.

Select that new edges and use Mark Seam.

Select all and subdivide it at your taste.

After sculpting the terrain, enter Edit Mode again. Change selection mode to Face.

Hit L over some part so select what you want to separate and separate it.

Image with the process here: